Looking for a gift for two little girls

So I'm seeing my two little cousins this weekend (both girls, agest 6 and 4). Her parents are very forward-thinking and support women's rights and equality, etc. And I fully support the way they're being raise... I love it! They took them to the march on Washington recently.

They're both brilliant beyond their years, and both love reading. I'm looking for some help in finding some appropriate gifts for them, with all of that in mind. Books that really help to solidify that idea that they're equal in every way. Stuff that will continue to boost their self confidence and self worth.

I'm rambling and super frazzled from work right now, so I hope this makes sense!